Systems and methods for welding electrodes

ABSTRACT

The invention relates generally to welding and, more specifically, to welding wires for arc welding, such as Gas Metal Arc Welding (GMAW) or Flux Core Arc Welding (FCAW). In one embodiment, a tubular welding wire for joining steel workpieces via arc welding includes a steel sheath disposed around a core. The core includes iron powder, iron titanium powder, silico-manganese powder, iron silicon powder, iron sulfide, graphite, rare earth compound, and a frit. The frit includes a Group I or Group II compound, silicon dioxide, and titanium dioxide. The graphite and the frit together comprise less than 10% of the core by weight.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. application Ser.No. 13/856,811, entitled “SYSTEMS AND METHODS FOR WELDING ELECTRODES,”filed Apr. 4, 2013, which claims priority from and the benefit of U.S.Provisional Application Ser. No. 61/625,488, entitled “SYSTEMS ANDMETHODS FOR WELDING ELECTRODES,” filed Apr. 17, 2012, which are herebyincorporated by reference in their entireties for all purposes.

BACKGROUND

The invention relates generally to welding and, more specifically, toelectrodes for arc welding, such as Gas Metal Arc Welding (GMAW) or FluxCore Arc Welding (FCAW).

Welding is a process that has become ubiquitous in various industriesfor a variety of applications. For example, welding is often used inapplications such as shipbuilding, offshore platform, construction, pipemills, and so forth. Certain welding techniques (e.g., Gas Metal ArcWelding (GMAW), Gas-shielded Flux Core Arc Welding (FCAW-G), and GasTungsten Arc Welding (GTAW)), typically employ a shielding gas (e.g.,argon, carbon dioxide, or oxygen) to provide a particular localatmosphere in and around the welding arc and the weld pool during thewelding process, while others (e.g., Flux Core Arc Welding (FCAW),Submerged Arc Welding (SAW), and Shielded Metal Arc Welding (SMAW)) donot. Additionally, certain types of welding may involve a weldingelectrode in the form of welding wire. Welding wire may generallyprovide a supply of filler metal for the weld as well as provide a pathfor the current during the welding process. Furthermore, certain typesof welding wire (e.g., tubular welding wire) may include one or morecomponents (e.g., flux, arc stabilizers, or other additives) that maygenerally alter the welding process and/or the properties of theresulting weld.

BRIEF DESCRIPTION

In one embodiment, a tubular welding wire includes a sheath and a core.Further, the core includes a carbon source and an agglomerate having aGroup I or Group II compound, silicon dioxide, and titanium dioxide.Additionally, the carbon source and the agglomerate together compriseless than 10% of the core by weight.

In another embodiment, a granular welding wire core having a carbonsource including graphite, carbon black, or lamp black. Further, thegranular core includes an agglomerate having potassium oxide or sodiumoxide, silicon dioxide, titanium dioxide, and manganese oxide. Further,the carbon source and the agglomerate together comprise less than 10% ofthe core by weight.

In another embodiment, a method of manufacturing a tubular welding wireincludes disposing a core within a metallic sheath. The core includes acarbon source and an agglomerate. Further, the agglomerate includes atleast one oxide of each of: a Group I or Group II metal, silicon, andmanganese. Additionally, the carbon source and the agglomerate togethercomprise less than 10% of the tubular welding wire by weight.

DRAWINGS

These and other features, aspects, and advantages of the presentinvention will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a block diagram of a gas metal arc welding (GMAW) system, inaccordance with embodiments of the present disclosure;

FIG. 2 is a cross-sectional view of a tubular welding electrode, inaccordance with embodiments of the present disclosure;

FIG. 3 is a process by which the tubular welding electrode may be usedto weld a workpiece, in accordance with embodiments of the presentdisclosure; and

FIG. 4 is a process for manufacturing the tubular welding electrode, inaccordance with embodiments of the present disclosure.

DETAILED DESCRIPTION

As mentioned, certain types of welding electrodes (e.g., tubular weldingwire) may include one or more components (e.g., flux, arc stabilizers,or other additives) that may generally alter the welding process and/orthe properties of the resulting weld. For example, the present weldingelectrode embodiments may include stabilizers, such as carbon compounds,alkali metal compounds, alkaline earth metal compounds, rare earthcompounds, and so forth. Additionally, as discussed below, certainstabilizing components of the disclosed welding electrodes may bepresent in the core of the welding electrodes in the form of anagglomerate. As discussed in detail below, providing one or morestabilizing components as an agglomerate enables the stabilizingcompounds to be delivered in a form that is better suited for the weldenvironment than the non-agglomerated compounds. For example, in certainembodiments, the disclosed arc stabilizing components may provide a“soft arc,” which may generally provide suitable heat to the workpieceto fuse portions of the workpiece and/or vaporize the coating (e.g., thezinc coating of galvanized workpieces), even thin workpieces, withoutresulting in burn-through. In certain embodiments, the “soft arc”provided by the one or more stabilizers of the presently disclosedwelding electrodes may enable improved welding of uncoated and coated(e.g., plated, galvanized, painted, aluminized, carburized, or similarlycoated) workpieces. Additionally, the present approach may be useful forwelding thinner workpieces, such as workpieces having a thickness lessthan 16 gauge (0.051 in.), less than 20 gauge (0.032 in.), less than 22gauge (0.25 in.), or approximately 24 gauge (0.02 in.).

It should be appreciated that, as used herein, the term “tubular weldingelectrode” or “tubular welding wire” may refer to any welding wire orelectrode having a metal sheath and a granular or powdered core, such asmetal-cored or flux-cored welding electrodes and wires. It should alsobe appreciated that the term “stabilizer” may be generally used to referto any component of the tubular welding wire that improves the qualityof the arc and/or weld, such as certain disclosed carbon sources, alkalimetal compounds, alkaline earth metal compounds, and rare earthcompounds.

Turning to the figures, FIG. 1 illustrates an embodiment of a gas metalarc welding (GMAW) system 10 that utilizes a welding electrode (e.g.,tubular welding wire) in accordance with the present disclosure. Itshould be appreciated that, while the present discussion may focusspecifically on the GMAW system 10 illustrated in FIG. 1, the presentlydisclosed welding electrodes may benefit any arc welding process (e.g.,FCAW, FCAW-G, GTAW, SAW, SMAW, or similar arc welding process) that usesa welding electrode. The welding system 10 includes a welding power unit12, a welding wire feeder 14, a gas supply system 16, and a weldingtorch 18. The welding power unit 12 generally supplies power to thewelding system 10 and may be coupled to the welding wire feeder 14 via acable bundle 20 as well as coupled to a workpiece 22 using a lead cable24 having a clamp 26. In the illustrated embodiment, the welding wirefeeder 14 is coupled to the welding torch 18 via a cable bundle 28 inorder to supply consumable, tubular welding wire (i.e., the weldingelectrode) and power to the welding torch 18 during operation of weldingsystem 10. In another embodiment, the welding power unit 12 may coupleand directly supply power to the welding torch 18.

The welding power unit 12 may generally include power conversioncircuitry that receives input power from an alternating current powersource 30 (e.g., an AC power grid, an engine/generator set, or acombination thereof), conditions the input power, and provides DC or ACoutput power via the cable 20. As such, the welding power unit 12 maypower the welding wire feeder 14 that, in turn, powers the welding torch18, in accordance with demands of the welding system 10. The lead cable24 terminating in the clamp 26 couples the welding power unit 12 to theworkpiece 22 to close the circuit between the welding power unit 12, theworkpiece 22, and the welding torch 18. The welding power unit 12 mayinclude circuit elements (e.g., transformers, rectifiers, switches, andso forth) capable of converting the AC input power to a direct currentelectrode positive (DCEP) output, direct current electrode negative(DCEN) output, DC variable polarity, pulsed DC, or a variable balance(e.g., balanced or unbalanced) AC output, as dictated by the demands ofthe welding system 10. It should be appreciated that the presentlydisclosed welding electrodes (e.g., tubular welding wire) may enableimprovements to the welding process (e.g., improved arc stability and/orimproved weld quality) for a number of different power configurations.

The illustrated welding system 10 includes a gas supply system 16 thatsupplies a shielding gas or shielding gas mixtures from one or moreshielding gas sources 17 to the welding torch 18. In the depictedembodiment, the gas supply system 16 is directly coupled to the weldingtorch 18 via a gas conduit 32. In another embodiment, the gas supplysystem 16 may instead be coupled to the wire feeder 14, and the wirefeeder 14 may regulate the flow of gas from the gas supply system 16 tothe welding torch 18. A shielding gas, as used herein, may refer to anygas or mixture of gases that may be provided to the arc and/or weld poolin order to provide a particular local atmosphere (e.g., to shield thearc, improve arc stability, limit the formation of metal oxides, improvewetting of the metal surfaces, alter the chemistry of the weld deposit,and so forth). In certain embodiments, the shielding gas flow may be ashielding gas or shielding gas mixture (e.g., argon (Ar), helium (He),carbon dioxide (CO₂), oxygen (O₂), nitrogen (N₂), similar suitableshielding gases, or any mixtures thereof). For example, a shielding gasflow (e.g., delivered via conduit 32) may include Ar, Ar/CO₂ mixtures,Ar/CO₂/O₂ mixtures, Ar/He mixtures, and so forth. For example, incertain embodiments, the shielding gas may be a mixture of 75% Ar and25% CO₂ or a mixture of 90% Ar and 10% CO₂.

Accordingly, the illustrated welding torch 18 generally receives thewelding electrode (i.e., the tubular welding wire), power from thewelding wire feeder 14, and a shielding gas flow from the gas supplysystem 16 in order to perform GMAW of the workpiece 22. Duringoperation, the welding torch 18 may be brought near the workpiece 22 sothat an arc 34 may be formed between the consumable welding electrode(i.e., the welding wire exiting a contact tip of the welding torch 18)and the workpiece 22. Additionally, as discussed below, by controllingthe composition of the welding electrode (i.e., the tubular weldingwire), the chemistry of the arc 34 and/or the resulting weld (e.g.,composition and physical characteristics) may be varied. For example,the welding electrode may include fluxing and/or alloying componentsthat may affect the mechanical properties of the weld. Furthermore,certain components of the welding electrode (i.e., welding wire) mayalso provide additional shielding atmosphere near the arc, affect thetransfer properties of the arc, and/or deoxidize the surface of theworkpiece, and so forth.

A cross-section of an embodiment of the presently disclosed welding wireis illustrated in FIG. 2. The tubular welding wire 50 illustrated inFIG. 2 includes a metallic sheath 52 that encapsulates a granular orpowdered core 54. The metallic sheath 52 may be manufactured from anysuitable metal or alloy (e.g., high-carbon steel, low-carbon steel, orother suitable metal or alloy). It should be appreciated that since themetallic sheath 52 may generally provide a portion of the filler metalfor the weld, the composition of the metallic sheath 52 may affect thecomposition of the resulting weld. As such, the metallic sheaths 52 mayinclude additives or impurities (e.g., carbon, alkali metals, manganese,nickel, copper, or similar compounds or elements) that may be selectedto provide desired weld properties.

The granular core 54 of the illustrated tubular welding wire 50 maygenerally be a compacted powder with a composition that, as discussedbelow, may include one or more stabilizing components. For example, tostabilize the arc 34, certain embodiments of the granular core 54 mayinclude one or more of: a carbon source, an alkali metal compound oragglomerate, an alkaline earth metal compound or agglomerate, and a rareearth compound. Further, in certain embodiments, the stabilizers (e.g.,a carbon source and one or more stabilizing agglomerates) may accountfor approximately 10% or less of granular core by weight. The variouscomponents of the granular core 54 may be disposed homogenously ornon-homogenously (e.g., in clumps or clusters 56) within the granularcore 54. As set forth in detail below, one or more of the stabilizingcomponents of the granular core 54 (e.g., one or more alkali metalcompounds and/or alkaline earth metal compounds) may be provided in theform of an agglomerate or frit within the granular core 54.Additionally, for certain welding electrode embodiments (e.g., ametal-cored welding electrode), the granular core 54 may include one ormore metals (e.g., iron, nickel, copper, high-carbon iron powder,ferro-molybdenum powder, or other suitable metals) that may provide atleast a portion of the filler metal for the weld. Examples of othercomponents that may be present within the tubular welding wire 50include other stabilizing, fluxing, and alloying components, such as maybe found in METALLOY X-CELTM welding electrodes available from IllinoisTool Works, Inc.

Generally speaking, in certain embodiments, the total percentage of thecombination of the stabilizers (e.g., one or more carbon sources, alkalimetal compounds, alkaline earth metal compounds, and/or rare earthcompounds) in the tubular welding wire 50 may be between approximately0.01% and approximately 10% by weight relative to the granular core 54or the entire tubular welding wire 50. For example, in certainembodiments, the total percentage of the combination of the one or morestabilizers may be between approximately 0.01% and approximately 8%,between approximately 0.05% and approximately 5%, or betweenapproximately 0.1% and approximately 4% by weight relative to thegranular core 54 or the entire tubular welding wire 50. It should beappreciated that, under the conditions of the arc 34, the components ofthe welding wire (e.g., the metal sheath 52, the granular core 54, andso forth) may change physical state, chemically react (e.g., oxidize,decompose, and so forth), or become incorporated into the weldsubstantially unmodified by the weld process.

The carbon source present in the granular core 54 and/or the metalsheath 52 may be in a number of forms and may stabilize the arc 34and/or increase the carbon content of the weld. For example, in certainembodiments, graphite, graphene, nanotubes, fullerenes or similarsubstantially sp²-hybridized carbon source may be utilized as the carbonsource in the tubular welding wire 50. Furthermore, in certainembodiments, graphene or graphite may be used to also provide othercomponents (e.g., moisture, gases, metals, and so forth) that may bepresent in the interstitial space between the sheets of carbon. In otherembodiments, substantially sp³-hybridized carbon sources (e.g., micro-or nano-diamond, carbon nanotubes, buckyballs) may be used as the carbonsource. In still other embodiments, substantially amorphous carbon(e.g., carbon black, lamp black, soot, or similar amorphous carbonsources) may be used as the carbon source. Furthermore, while thepresent disclosure may refer to this component as a “carbon source,” itshould be appreciated that the carbon source may be a chemicallymodified carbon source that may contain elements other than carbon(e.g., oxygen, halogens, metals, and so forth). For example, in certainembodiments, the tubular welding wire 50 may include a carbon blackcarbon source (e.g., in the granular core 54 and/or the metallic sheath54) that may contain a manganese content of approximately 20%.Additionally, in certain embodiments, the carbon source may account forbetween approximately 0.01% and 9.9%, between approximately 0.05% and5%, between approximately 0.1% and 3%, between approximately 0.25% and2%, between approximately 0.4% and 1%, or approximately 0.5% of thegranular core 54 by weight.

Additionally, the tubular welding wire 50 may also include one or morealkali metal and/or alkaline earth metal compounds to stabilize the arc34. That is, the granular core 54 of the tubular welding wire 50 mayinclude one or more compounds of the Group 1 and Group 2 elements, i.e.,lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs),beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), or barium(Ba). A non-limiting list of example compounds include: Group 1 (i.e.,alkali metal) and Group 2 (i.e., alkaline earth metal) silicates,titanates, manganese titanate, alginates, carbonates, halides,phosphates, sulfides, hydroxides, oxides, permanganates, silicohalides,feldspars, pollucites, molybdenites, and molybdates. For example, in anembodiment, the granular core 54 of the tubular welding wire 50 mayinclude potassium manganese titanate, potassium sulfate, sodiumfeldspar, potassium feldspar, and/or lithium carbonate. Similar examplesof carbon sources and alkali metal compounds that may be used aredescribed in U.S. Pat. No. 7,087,860, entitled “STRAIGHT POLARITY METALCORED WIRES,” and U.S. Pat. No. 6,723,954, entitled “STRAIGHT POLARITYMETAL CORED WIRE,” which are both incorporated by reference in theirentirety for all purposes. Furthermore, in certain embodiments, theaforementioned Group 1 and Group 2 compounds may be disposed directlywithin the core 54 of the tubular welding wire 50, while in otherembodiments, the aforementioned Group 1 and Group 2 compounds may beused to form an agglomerate, as set forth in detail below. It should beappreciated that certain of the aforementioned compounds may beconverted into another type of compound during the agglomeration process(e.g., potassium carbonate may become potassium oxide).

Additionally, the tubular welding wire 50 may also include otherstabilizing components. In particular, rare earth compounds (e.g., rareearth silicides, rare earth oxides, and so forth) may generally providestability to the arc 34 and may affect the properties of the resultingweld. Accordingly, certain embodiments of the presently disclosedwelding wire may include one or more rare earth compounds (e.g.,compounds of lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium(Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), orother suitable rare earth metals). A non-limiting list of examplecompounds include: rare earth silicides, oxides, silicates, titanates,alginates, carbonates, halides, phosphates, sulfides, hydroxides,permanganates, silicohalides, feldspars, pollucites, molybdenites, andmolybdates. For example, in certain embodiments, the tubular weldingwire 50 may use rare earth silicides, such as the Rare Earth Silicide(e.g., available from Miller and Company of Rosemont, Illinois), whichmay include rare earth elements (e.g., cerium). By further example, incertain embodiments, the tubular welding wire 50 may include one or moreoxides of a rare earth element (e.g., cerium oxide, lanthanum oxide,samarium oxide and so forth) to provide stability to the arc 34 duringthe welding operation. As discussed in detail below, in certainembodiments, the rare earth compounds used in conjunction with anagglomerate (e.g., with an alkali metal compound and/or an alkalineearth metal compound) to provide a combined stabilizing effect to thearc.

Furthermore, the tubular welding wire 50 may, additionally oralternatively, include other elements and/or minerals to control thechemistry of the resulting weld. For example, in certain embodiments,the granular core 54 and/or the metallic sheath 52 of the tubularwelding wire 50 may include certain elements (e.g., titanium, manganese,zirconium, fluorine, or other elements) and/or minerals (e.g., pyrite,magnetite, and so forth). By specific example, certain embodiments mayinclude zirconium silicide, nickel zirconium, or alloys of titanium,aluminum, and/or zirconium in the granular core 54. In particular,sulfur containing compounds, including various sulfide, sulfate, and/orsulfite compounds (e.g., such as molybdenum disulfide, iron sulfide,manganese sulfite, barium sulfate, calcium sulfate, or potassiumsulfate) or sulfur-containing compounds or minerals (e.g., pyrite,gypsum, or similar sulfur-containing species) may be included in thegranular core 54 to improve the quality of the resulting weld byimproving bead shape and facilitating slag detachment, which may beespecially useful when welding galvanized workpieces, as discussedbelow. Furthermore, in certain embodiments, the granular core 54 of thetubular welding wire 50 may include multiple sulfur sources (e.g.,manganese sulfite, barium sulfate, and pyrite), while other embodimentsof the tubular welding wire 50 may include only a single sulfur source(e.g., pyrite or iron sulfide) without including a substantial amount ofanother sulfur source (e.g., potassium sulfate).

Furthermore, in certain embodiments of the presently disclosed tubularwelding wire 50, a number of stabilizing components (e.g., one or morealkali metal compounds and/or alkaline earth metal compounds) may bepresent in the granular core 54 as an agglomerate or frit. For example,certain embodiments of the tubular welding wire 50 may include anagglomerate or frit having one or more of an alkali metal compound andan alkaline earth metal compound, together with one or more binding(e.g., potassium silicate, sodium silicate, or combinations thereof)and/or drying agents (e.g., lithium fluoride). The term “agglomerate” or“frit,” as used herein, refers to a mixture of compounds that have beenfired or heated in a calciner or oven such that the components of themixture are in intimate contact with one another. It should beappreciated that the agglomerate may have subtly or substantiallydifferent chemical and/or physical properties than the individualcomponents of the mixture used to form the agglomerate. For example, incertain embodiments, mixing and then agglomerating potassium carbonate,sand, and rutile may provide an agglomerate that includes a mixture ofpotassium oxide, silica, and titanium dioxide after firing.

Agglomerating certain stabilizing components (e.g., one or more alkalimetal compounds, alkaline earth metal compounds, or any other suitablestabilizing components) into a frit, as presently disclosed, may deliverthese stabilizing compounds in a form that is better suited for the weldenvironment than the non-agglomerated compounds. While not desiring tobe bound to theory, one manner in which the agglomerate may improve thechemical and/or physical properties of the granular core 54 is byensuring that the agglomerated stabilizing components remain dry (e.g.,absorbing little or no moisture from the atmosphere or surroundingenvironment) before being introduced into the conditions of the weldingarc 34. Further, another manner in which the agglomerate may improve thechemical and/or physical properties of the granular core 54 is byenabling the stabilizing components to have particular relative ratiosand localized concentrations during delivery to the welding arc 34.

In certain embodiments, the granular core 54 of the tubular welding wire50 may include an agglomerate having one or more alkali metal compounds(e.g., potassium oxide, sodium oxide, or another suitable alkali metalcompound) and/or one or more alkaline earth metal compounds (e.g.,magnesium oxide, calcium oxide, or another suitable alkaline earth metalcompound). For example, in certain embodiments, the granular core 54 mayinclude an agglomerate including a combination of potassium oxide andsodium oxide. In certain embodiments, the granular core 54 of thetubular welding wire 50 may also include an agglomerate comprising otheroxides (e.g., silicon dioxide, titanium dioxide, manganese dioxide, orother suitable metal oxides) and/or certain drying or binding agents(e.g., silicates, lithium fluoride, and so forth) as well. For example,one embodiment of a tubular welding wire 50 may include an agglomerateincluding a mixture of potassium oxide, silica, and titania. By specificexample, certain embodiments of a tubular welding wire 50 may include anagglomerate in the granular core 54 (e.g., between approximately 1% andapproximately 10% of the granular core, or approximately 2% of thegranular core), and the agglomerate may include a mixture of potassiumoxide (e.g., between approximately 22% and 25% by weight of stabilizingagglomerate), silica (e.g., between approximately 10% and 18% by weightof the stabilizing agglomerate), titania (e.g., between approximately38% and 42% by of weight the stabilizing agglomerate), and manganeseoxide or manganese dioxide (e.g., between approximately 16% and 22% byweight of the stabilizing agglomerate).

In certain embodiments, the granular core 54 of the tubular welding wire50 may include an agglomerate having one or more alkali metal compounds(e.g., sodium oxide, potassium oxide, or other suitable alkali metalcompound) and zero or more alkaline earth metal compounds (e.g.,magnesium oxide, calcium oxide, or other suitable alkaline earth metalcompounds) that together account for between approximately 5% and 75% ofthe weight of the agglomerate. In other embodiments, the one or morealkali metal compounds and zero or more alkaline earth metal compoundsmay account for between approximately 5% and 95% of the agglomerate byweight. Furthermore, in certain embodiments, other chemical and/orphysical factors (e.g., maximizing alkali metal and/or alkaline earthmetal loading, acidity, stability, and/or hygroscopicity of theagglomerate) may be considered when selecting the relative amounts ofeach component present in the agglomerate. Additionally, in certainembodiments, the agglomerate may account for between approximately 0.01%and approximately 9.9%, between approximately 0.05% and approximately5%, between approximately 0.1% and approximately 4%, betweenapproximately 1% and approximately 3%, between approximately 1.5% andapproximately 2.5%, or approximately 2% of the granular core 54 byweight.

Generally speaking, the tubular welding wire 50 may generally stabilizethe formation of the arc 34 to the workpiece 22. As such, the disclosedtubular welding wire 50 may improve deposition rates while reducingsplatter during the welding process. It should further be appreciatedthat the improved stability of the arc 34 may generally enable thewelding of coated metal workpieces. A non-limiting list of examplecoated workpieces includes painted, sealed, galvanized, galvanealed,plated (e.g., nickel-plated, copper-plated, tin-plated, or electroplatedor chemically plated using a similar metal), chromed, nitrite-coated,aluminized, or carburized workpieces. For example, in the case ofgalvanized workpieces, the presently disclosed tubular welding wire 50may generally improve the stability and the penetration of the arc 34such that a good weld may be achieved despite the zinc coating on theoutside of the workpiece 22. Additionally, by improving the stability ofthe arc 34, the disclosed tubular welding wire 50 may generally enablethe welding of thinner workpieces than may be possible using otherwelding electrodes. For example, in certain embodiments, the disclosedtubular welding wire 50 may be used to weld metal having anapproximately 16-, 20-, 22-, 24-gauge, or even thinner workpieces.

Furthermore, the disclosed tubular welding wire 50 may also be combinedwith certain welding methods or techniques (e.g., techniques in whichthe welding electrode moves in a particular manner during the weldoperation) that may further increase the robustness of the weldingsystem 10 for particular types of workpieces. For example, in certainembodiments, the welding torch 18 may be configured to cyclically orperiodically move the electrode in a desired pattern (e.g., a circular,spin arc, or serpentine pattern) within the welding torch 18 in order tomaintain an arc 34 between the tubular welding wire 50 and the workpiece22 (e.g., only between the sheath 52 of the tubular welding wire 50 andthe workpiece 22). By specific example, in certain embodiments, thedisclosed tubular welding wire 50 may be utilized with welding methodssuch as those described in U.S. patent application Ser. No.13/681,687,entitled “DC ELECTRODE NEGATIVE ROTATING ARC WELDING METHODAND SYSTEM,” which is incorporated by reference herein in its entiretyfor all purposes. It should be appreciated that such welding techniquesmay be especially useful when welding thin workpieces (e.g., having 16-,20-, 22-, 24-gauge, or even thinner thickness), as mentioned above.

FIG. 3 illustrates an embodiment of a process 60 by which a workpiece 22may be welded using the disclosed welding system 10 and tubular weldingwire 50 (e.g., tubular welding electrode 50). The illustrated process 60begins with feeding (block 62) the tubular welding electrode 50 (i.e.,the welding wire 50) to a welding apparatus (e.g., welding torch 18).Additionally, the process 60 includes providing (block 64) a shieldinggas flow (e.g., 100% argon, 75% argon/25% carbon dioxide, 90% argon/10%helium, or similar shielding gas flow) near the contact tip of thewelding apparatus (e.g., the contact tip of the torch 18). In otherembodiments, welding systems may be used that do not use a gas supplysystem (e.g., such as the gas supply system 16 illustrated in FIG. 1)and one or more components (e.g., aluminum, iron, or magnesium oxides)of the tubular welding electrode 50 may provide a shielding gascomponent. Next, the tubular welding electrode 50 may be brought near(block 66) the workpiece 22 such that an arc 34 may be formed betweenthe tubular welding electrode 50 and the workpiece 22. It should beappreciated that the arc 34 may be produced using, for example, a DCEP,DCEN, DC variable polarity, pulsed DC, balanced or unbalanced AC powerconfiguration for the GMAW system 10. Furthermore, as mentioned above,in certain embodiments, the tubular welding electrode 50 may becyclically or periodically moved (block 68) relative to the workpiece 22according to a particular pattern and/or geometry (e.g., spinning arc,whirling pattern, or serpentine pattern) such that the arc 34 may bemaintained (e.g., substantially between the metal sheath 52 of thetubular welding electrode 50 and the workpiece 22) during the weldingprocess. Additionally, in certain embodiments, the tubular weldingelectrode 50 and/or the cyclical motion of the tubular welding electrode50 during welding may generally enable the welding of thinner (e.g.,less than 20 gauge) workpieces as well as painted, galvanized,galvanealed, plated, aluminized, chromed, carburized, or other similarcoated workpieces.

FIG. 4 illustrates an embodiment of a process 70 by which the tubularwelding wire 50 may be manufactured. The process 70 begins with a flatmetal strip being fed (block 72) through a number of dies that shape thestrip into a partially circular metal sheath 52 (e.g., producing asemicircle or trough). After the metal strip has been at least partiallyshaped into the metal sheath 52, it may be filled (block 74) with thegranular core material 54. Accordingly, the partially shaped metalsheath 52 may be filled with various powdered fluxing and alloyingcomponents (e.g., iron oxide, zinc metal, or similar fluxing and/oralloying components). Additionally, in certain embodiments, thestabilizing components (e.g., the one or more carbon sources, and/or oneor more alkali metal compounds, and/or one or more alkaline earth metalcompounds, and/or one or more rare earth metal compounds) may be addedsuch that together they comprise less than 10% of the tubular weldingwire 50 and/or the granular core material 54 by weight. Additionally, asset forth above, in certain embodiments, an alkali metal compound,and/or an alkaline earth metal compound may be present in the granularcore 54 in the form of an agglomerate. Furthermore, in certainembodiments, other components (e.g., rare earth silicide, magnetite,titanate, pyrite, iron powders, and/or other similar components) mayalso be present in the granular core 54 being added to the partiallyshaped sheath.

By specific example, in an embodiment, the granular core 54 may include(by weight) approximately 71.6% iron powder, approximately 1.1% irontitanium powder, approximately 17.1% silico-manganese powder,approximately 4.0% iron silicon powder, approximately 0.4% iron sulfide(e.g., pyrite), approximately 0.5% graphite, approximately 3.3% rareearth silicide, and approximately 2% of an agglomerate. Further, thesilico-manganese powder, also known as ferro-manganese silicon, mayinclude approximately 62% manganese, approximately 30% silicon, andapproximately 8% iron by weight of the silico-manganese powder.Additionally, in such an embodiment, the agglomerate may include (byweight of the agglomerate) between approximately 22% and approximately25% potassium oxide and/or sodium oxide, between approximately 16% andapproximately 22% manganese oxide or manganese dioxide, betweenapproximately 10% and approximately 18% silicon dioxide, and betweenapproximately 38% and approximately 42% titanium dioxide. Further, incertain embodiments, as set forth above, a rare earth metal silicide ora rare earth metal oxide may be included in the granular core 54 alongwith the agglomerate, for example, to stabilize the arc. Certain otherembodiments of the granular core 54 may have a similar formula, but mayvary (e.g., by approximately 5% or less) from the values listed above.

Once the components of the granular core 54 have been added to thepartially shaped metal sheath 52, the partially shaped metal sheath 52may then be fed through (block 76) one or more devices (e.g., dies) thatmay generally close the metal sheath 52 such that it substantiallysurrounds the granular core material 54 (e.g., forming a seam 58).Additionally, the closed metal sheath 52 may subsequently be fed through(block 78) a number of drawing devices (e.g., drawing dies) to reducethe diameter of the tubular welding wire 50 by compressing the granularcore material 54.

While only certain features of the invention have been illustrated anddescribed herein, many modifications and changes will occur to thoseskilled in the art. It is, therefore, to be understood that the appendedclaims are intended to cover all such modifications and changes as fallwithin the true spirit of the invention.

1. A tubular welding wire for joining steel workpieces via arc welding,comprising: a steel sheath disposed around a core, wherein the corecomprises: iron powder; iron titanium powder; silico-manganese powder;iron silicon powder; iron sulfide; graphite; rare earth compound; and afit comprising a Group I or Group II compound, silicon dioxide, andtitanium dioxide, wherein the graphite and the frit together compriseless than 10% of the core by weight.
 2. The tubular welding wire ofclaim 1, wherein the graphite and the frit together comprise between0.05% and 5% of the core by weight.
 3. The tubular welding wire of claim2, wherein the graphite and the frit together comprise between 1% and2.5% of the core by weight.
 4. The tubular welding wire of claim 1,wherein the Group I or Group II compound comprises a Group I oxide, aGroup II oxide, a Group I fluoride, or Group II fluoride.
 5. The tubularwelding wire of claim 4, wherein the Group I or Group II compoundcomprises potassium oxide, sodium oxide, or a combination thereof. 6.The tubular welding wire of claim 1, wherein the frit comprises at leastone oxidized form of manganese.
 7. The tubular welding wire of claim 1,wherein the rare earth compound comprises a rare earth metal oxide. 8.The tubular welding wire of claim 7, wherein the rare earth metal oxidecomprises cerium oxide, lanthanum oxide, or samarium oxide.
 9. Thetubular welding wire of claim 1, wherein the rare earth compoundcomprises a rare earth metal silicide.
 10. The tubular welding wire ofclaim 9, wherein the rare earth metal silicide comprises ceriumsilicide.
 11. The tubular welding wire of claim 1, wherein iron sulfideis the only sulfur source of the tubular welding wire.
 12. The tubularwelding wire of claim 1, wherein the silico-manganese powdersubstantially comprises 62% manganese, 30% silicon, and 8% iron byweight of the silico-manganese powder.
 13. The tubular welding wire ofclaim 1, wherein the frit substantially comprises between 22% and 25%potassium oxide and/or sodium oxide, between 16% and 22% manganese oxideor manganese dioxide, between 10% and 18% silicon dioxide, and between38% and 42% titanium dioxide by weight of the frit.
 14. A tubularwelding wire for arc welding a coated steel workpiece, wherein thetubular welding wire comprises: a steel sheath disposed around a core,wherein the core comprises graphite and a frit, wherein the fritconsists essentially of: sodium oxide or potassium oxide; manganeseoxide or manganese dioxide; silicon dioxide; and titanium dioxide; andwherein the graphite and the frit together comprise less than 10% of thecore by weight, and wherein, during arc welding, the tubular weldingwire produces a soft arc that provides suitable heat to vaporize acoating of the coated steel workpiece and to fuse portions of the coatedsteel workpiece without burn-through.
 15. The tubular welding wire ofclaim 14, wherein the core comprises a rare earth compound and ironsulfide.
 16. The tubular welding wire of claim 15, wherein the corecomprises:
 0. 5% graphite; 2% of the frit; 3% rare earth silicide; and0.4% iron sulfide.
 17. A tubular welding wire for arc welding a coatedsteel workpiece, wherein the tubular welding wire comprises: a steelsheath disposed around a core, wherein the core consists essentially of:alloying components; a carbon source; a sulfur source; a rare earthcompound; and a frit consisting essentially of: sodium oxide orpotassium oxide; manganese oxide or manganese dioxide; silicon dioxide;and titanium dioxide; and wherein, during arc welding, the tubularwelding wire produces a soft arc that provides suitable heat to vaporizea coating of the coated steel workpiece and to fuse portions of thecoated steel workpiece without burn-through.
 18. The tubular weldingwire of claim 17, wherein the carbon source is graphite, the sulfursource is iron sulfide, and the rare earth compound is rare earthsilicide.
 19. The tubular welding wire of claim 18, wherein the alloyingcomponents comprise: iron silicon powder, iron titanium powder,silico-manganese powder, and iron powder.
 20. The tubular welding wireof claim 19, wherein the core comprises: 72% iron powder; 1% irontitanium powder; 17% silico-manganese powder; 4% iron silicon powder; 4%iron sulfide;
 0. 5% graphite; 3% rare earth silicide; and 2% of the fritby weight.